another port question

[quins90lac 10+ year member]

ok i all ready got my box built and tuned to 35hz seams to be the sweet spot for my subs .so my question is if you say tune a box to 35hz dose that mean it will play notes from 0hz to 35hz or from 35hz on up .i only ask cause i play say like a 50hz note my rear veiw mior vibrates like crazy so im thinking 35hz on up

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[thegreatestpenn 5,000+ posts]

The box doesn't play the notes, the subwoofer does. This only means the box will peak around 35Hz, but it'll play every other frequency the sub wants to play

 

[CarAudioGuru 10+ year member]

Actually the box does it ALL at and below 35 Hz. Take an audio generator and sweep your box and watch how far the woofer moves the lower you go.

At some point (near 35Hz) the woofer will STOP moving and the port does all the work.

Thats why the port needs to be pretty large in area so it can move more air.

Problem is as the port area increases so does port length.

Pretty interesting to test.

 

[kmanian 5,000+ posts]

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[kush-divinity 10+ year member]

At some point (near 35Hz) the woofer will STOP moving and the port does all the work.

This is funny. Thank you for making me laugh, now go commit ******* please, and very slowly.

 

[CarAudioGuru 10+ year member]

Testing subwoofers is actually very interesting.

These articles and webpages tell a lot more about vented enclosures.

http://www.ddaudio.com/dd/caraudio/enclosureInfo/portInfo.asp

A REALLY good one for anyone building or designing subwoofers

http://www.diysubwoofers.org/prt/

And for you SPL guys, this article is really good

http://www.diysubwoofers.org/car/caraudiospl.htm

Now if you MIS-align a vented box, things get really ugly FAST right at FsB (vent frequency) of the enclosure.

But typically SPL guys are ALWAYS building Mis-Aligned *chebyshev" type enclosures - on purpose, thats why they POUND!

But, as you read you'll see that a port actually moves as much air as the woofer, if not more.

And as the woofer moves less, the port moves more. Depends on design, tuning, port dimensions, etc.

Super important to design your vented boxes correctly.

Hope that helps